1. Field of the Invention
This invention relates to a method of non-contact conveyance of a long belt-shaped support of plastic film, paper or the like (hereinafter referred to as "a web"). More particularly the invention relates to a method of conveying a web in a non-contact manner in the manufacture of a photographic photo-sensitive material such as a photographic film or print paper, a photomechanical material, a magnetic recording material such as a magnetic recording tape, or a recording material such as a pressure-sensitive sheet or heat-sensitive copying sheet.
2. Background of the Invention
Heretofore, a roller system has been extensively employed to convey a web of plastic film or paper. However, since in the roller system the web is conveyed while being in contact with the rollers, depending on the operating conditions, the web may be scratched or creased, i.e., the product may be damaged. Especially in the case of a web having coated films on both its sides, its quality is lowered when conveyed by the roller system. In order to overcome these difficulties, a method has been employed in which a jetted air stream is applied to a web so that the web is conveyed while being floated, i.e., it is conveyed in a non-contact manner.
FIG. 1 is a sectional side view showing a conventional method of conveying a web in a non-contact manner.
In the conventional method most extensively employed, as shown in FIG. 1, static pressure support type air jetting boxes 3 are arranged alternately on both sides of a web 1. Air streams are jetted through surfaces 5 of the air jetting boxes which are confronted with the web in such a manner that the jetted air streams are perpendicular to the web 1, thus floating the web in the form of a belt which is wavy in the direction of transport. In the method, in order to convey a web stably, it is essential to carefully design the configuration and dimension of the air jetting boxes 3 and the arrangement or position of air jetting outlets 4. Some of these conditions have been disclosed by Japanese Patent Application (OPI) No. 72847/1979. That is, the air jetting outlets 4 formed along two edges of each air jetting box 3 are slits through which air streams are jetted perpendicular to the air jetting surface. The transport of the web 1 is stabilized when W.gtoreq.P/6 is satisfied. In this expression, W is the distance between front and rear air jetting outlets 4a and 4b, and P is the distance between two adjacent corresponding positions where the pressures of the air streams act on the web 1 (that is, P is the pitch between two adjacent air jetting boxes on the same side of the web 1). In addition, it has been also disclosed that W should be relatively small (preferably not more than 1/5 of the width of the web). In conclusion, the condition for conveying a web stably is that the distance P is small.
As is apparent from the above description, in the conventional web conveying apparatus it is necessary to provide a number of air jetting boxes and accordingly to jet a large quantity of air. As a result, the equipment cost and the running cost are correspondingly increased.